Are there countries or topics you will not collect?

Well....angore - I like history and Prince Diana is part of history but like you probably wished to say......I do not like Countries abusing of her
!!   for $$$$ and stamps !

Good start to this thread !

René

Sharjah, Mutewakelite Yemen, Japan, Redonda, Grenadines.
I should admit that I somehow find a place for any stamps, even from those countries, but I do not seek them out.

Great question!

I made a decision, back when I was a teenager with limited financial resources and had to make hard choices on what to buy, to forego the Eastern European countries which were flooding the market at the time. I have stuck to that decision, although for very special cases I have gotten some stamps from them (like my avatar stamp which is a Soviet issue), but these are rare exceptions. Later, once I started spending serious money on my collection and was pondering the large selections you can find at online vendors, I had to come up with a priority system to help me choose what to buy. So I devised a system in which each stamp lot receives 3 "priority" rankings, one according to country, one according to thematic interest, and a third according to price. Then I add these three numbers up and the lots with the lowest total have the highest priority. This is not a perfect system, so I've tried to tweak it by adding the numbers in multiple ways, and I use a combination of these sums to guide my purchasing. Which does not preclude falling in love with a stamp set and going for that above the others from time to time, of course.

So the system goes:

For countries:
Rank 1: My main collecting interests: France, Canada (and former provinces), USA, Guatemala, Africa (all), St-Pierre-et-Miquelon, Guadeloupe, Martinique, French Guiana, Inini, TAAF, UN (all administrations), Syria (UAR period only), Palestine (overprinted Egyptian stamps only).
Rank 2: Associated to the above: Andorra (both administrations), Monaco, Saarland, Wallis-and-Futuna, New Caledonia, French Polynesia, French Indochina, French India, French Offices in China.
Rank 3: Germany (FRG, II. and III. Reichs, Weimar Republic, Berlin), German states, German colonies, Western German Allied occupation zones, Memel (French and German overprinted issues only).
Rank 4: Greenland, Rest of Western Europe, Rest of Oceania.
Rank 5: Rest of the Americas, Rest of Asia, Cyprus, Turkey.
Rank 6: Eastern Europe, Soviet Republics, Israel, Turkish Cyprus, Eastern German occupation zones, DDR.

For themes:
Rank 1: Science and technology, Nobel Prize winners, Space and astronomy, Northern and Southern lights, petroglyphs and prehistoric art.
Rank 2: Stamps-on-stamps, flags, maps.
Rank 3: Currency on stamps, Montreal (particularly Expo 67 and 76 Olympics issues), Jules Verne, Victor Hugo, Europa issues, non-rectangular shapes, errors and oddities, perfins, anything else of "special interest" to me. And some stamp themes that the kids like, although these have changed with time, but have included: certain story/movie characters, snails, penguins, rainbows, seahorses. Or related to some of my wife's favourite things: Klimt, Salzburg, Vienna.
Rank 4: Artsy stamps (usually large format reproductions of paintings or sculptures), other stamps where the engraving work is of great quality.
Rank 5: All other stamps that appear in my catalogs.
Rank 6: Everything else.

For price (per stamp, in units of the currency of the country I am ordering from, i.e. EUR, CAD, or USD):
Rank 1: Up to 2
Rank 2: 2 to 5
Rank 3: 5 to 10
Rank 4: 10 to 20
Rank 5: 20 to 50
Rank 6: 50 to 150
Rank 7: 150 to 300 (I usually do not even consider stamps above 300$, too rich for my blood)

With these numbers I build large Excel spreadsheets where I enter all the stamp lots I am interested in so that I can order them easily and play around with the sorting function to decide what I do buy. For a lot to interest me, it must contain at least one stamp with a score below Rank 4 in either the country or the theme. Rank 6 for either can be disqualifying, but these are individual judgment calls. Not the only condition, but necessary for making it on the spreadsheet. It's not the simplest system, but considering my spreadsheets contain several thousand stamp lots adding up to more than 100K$ in purchasing price, I needed something!

hrdoktorx - wow, I am amazed with your clearly defined and almost mathematical strategy for your collection! Must be quite complex when going shopping then, but at least you'll get what you really want. This must require an impressing determination and sense for details! Personally I am kind of the opposite from yourself - I am opportunistic and simply shop what my stampy-heart desires there and then